If you are replacing an existing one, do not necessarily just replace it with one the same size. It might be too large. You can achieve the best comfort by having it properly sized. If the heat load calculations are in-between two generally available sizes, you'll be more comfortable usually with the smaller one. The reason for this is that a properly sized one will run longer, pulling more humidity out of the air. Dryer air feels more comfortable than the same temperature air with a high humidity. Ideally, the thing would run continuously.

If you are going to change the furnace or air handler, the next big thing you can do is opt for a variable speed fan. Trane advertised awhile ago that in the same house, with the same a/c unit, just switching the fan to a multiple speed unit allowed it to extract enough extra moisture from the house over a season to fill an average backyard swimming pool. By running slowly when starting up, the air gets colder, extracting more moisture. It would only ramp up to high speed if it needed to run for over a particular time, and it did it in stages. When it stopped, is also slowly dropped in speed, extracting all of the energy you put into the coil.

Hi all, before I start to call contractors I would like to know what A/C brands are best or at least what to avoid, any opinions or sources I might use to identify.

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I really appreciate all feedback & opinions, especially the "boring" details (I'm an engineer type). I should mention that this house is my first 2 storey & IMHO may need to be reducted or zoned or both.

I'm trying to get enough info to sort out the guys that "know their stuff" from the ones that just want a "slamdunk".